Oil content in a European x Chinese rapeseed population: QTL with additive and epistatic effects and their genotype-environment interactions

Rapeseed (Brassica napus L.) is one of the most important oilseed crops both in Europe and in China. The objective of this study was to investigate whether the European and the Chinese gene pools of winter oilseed rape contain different alleles for high seed oil content. A linkage map of rapeseed comprising 125 SSR markers and covering 1196-cM genome length was constructed from an F1 derived doubled haploid (DH) population from a cross between the German cultivar Sollux and the Chinese cultivar Gaoyou, both selected for high oil content. In total, 282 DH lines were evaluated in replicated field experiments in four environments, two each in Germany and in China. QTL were mapped and their additive and epistatic effects as well as interactions with environments were estimated by a mixed model approach implemented in the mapping software QTLMapper. Eight QTL with additive effects and nine pairs of loci with additive x additive epistasis were detected, which together accounted for 80% of the phenotypic variation. The alleles increasing oil content were dispersed between the parents, which explained the transgressive segregation observed: seven DH lines surpassed the better parent by more than 3% oil content. Five of the eight QTL with additive effects showed significant genotype x environment interactions, and 10 additional QTL with genotype x environment interactions, but no significant additive main effect were observed. Epistatic interactions mainly occurred between QTL which also showed additive effects or additive x environment interactions. In conclusion, a marker assisted selection to recombine positive alleles from European and Chinese material is a powerful approach to further increase the oil content of rapeseed, but epistatic effects and genotype x environment interactions have to be considered.